As a conventional sensor device for detecting a very small amount of an analyte, an enzyme electrode immunosensor is known. The sensor uses an immobilized antibody, a labeled antibody to which an enzyme is linked, and an electrode, to detect an analyte, which is linked to the immobilized antibody, where the labeled antibody linked to the analyte is a subject to be detected. The amount of the analyte is detected as a change in the current produced by oxidation and reduction of a product by an enzyme reaction using the electrode. FIG. 2 shows a conventional enzyme electrode immunosensor. As shown in FIG. 2, in the conventional enzyme electrode immunosensor, antibodies 102 are immobilized on the entirety of a bottom surface of a detection cell 101. Analyte molecules (antigens) 103 in a specimen are diffused in a solution within the cell, and reach and specifically bind to the immobilized antibodies 102. A labeled antibody 105 linked to an enzyme 104 is allowed to bind additionally to the analyte 103, resulting in formation of a sandwich complex. Excess antigens and labeled antibodies are washed out before adding a reaction solution 106 containing a substrate 107 for an enzyme reaction. The substrate 107 is converted to an enzyme reaction product 108 by action of the enzyme. The enzyme reaction product 108 is further subjected to oxidation and reduction by an electrode 3, thereby detecting the analyte.
The potential of the electrode needs to be held at a predetermined potential for the purpose of electrochemical oxidation and reduction of the enzyme reaction product 108 (not shown in FIG. 2). Therefore, the potential of the electrode for oxidation and reduction is set to be a potential based on the potential of a reference electrode placed in the reaction solution as a reference potential.
Although such a conventional enzyme electrode immunosensor device advantageously has a relatively simple structure, detection rate and detection sensitivity may not be obtained to sufficient extent in a practical sense for some subjects to be detected. Some sensor devices employ a labeled antibody labeled with a fluorescent dye instead of an enzyme. Unfortunately, detection of fluorescence complicates the procedure. The present invention is provided to solve the problems of the above-described conventional sensor devices. The object of the present invention is to eliminate the above-described problems.
the potential of the electrode for oxidation and reduction is set to be the potential of a reference electrode placed in the reaction solution as a reference potential